Optical system adjusting method for energy beam apparatus

ABSTRACT

A method for adjusting an optical system of an energy beam apparatus by using a mark signal that is obtained by one-dimensionally or two-dimensionally scanning a mark on a sample with an energy beam. The mark has a one-dimensional or two-dimensional periodic structure. A first mark signal is detected by scanning the mark with a beam. The mark is set on the optical axis of the optical system. A second mark signal is detected by scanning the mark with a beam. The mark is located at a position that is deviated from the optical axis. A deviation of a deflection position is determined based on a phase difference between the first and second mark signals.

This is a division of U.S. patent application Ser. No. 10/602,701, filedJun. 25, 2003, now U.S. Pat. No. 6,781,680, which is a divisionalapplication of U.S. patent application Ser. No. 09/533,815, filed Mar.24, 2000, now U.S. Pat. No. 6,606,149 B1, issued Aug. 1 , 2003, all ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical system adjusting method inan energy beam apparatus, and more particularly, the invention relatesto an optical system adjusting method in an electron beam lithographyapparatus that is used to form a fine pattern on a wafer.

2. Discussion of the Background

In the electron beam lithography used in recent semiconductormanufacturing processes, to increase the throughput, variable shaping orcharacter projection type electron beam lithography apparatuses are usedin which writing is performed by generating a beam having across-section of a rectangle, a triangle, or an arbitrary pattern inaddition to the circular beam used in previous apparatuses. In this typeof apparatus, because of the miniaturization and the increased accuracyof the pattern formation, the beam dimensions and position must be moreaccurate.

One condition to be satisfied for increasing accuracy in beam dimensionsand position is that the optical axis of a beam and the axis of a lensshould coincide with each other. For example, this condition issatisfied in a manner shown in FIG. 11, which shows an exemplary beammeasurement using a conventional mark. A fine mark 112 is scanned with abeam 111, and a relative positional relationship between a scanningregion and the mark 112 is determined based on a resulting reflectedelectron signal. Adjustments are made by using an alignment coil so thatthis positional relationship does not vary, even if the degree of lensmagnetic excitation is changed.

The accuracy of an electron beam deflection position must also be veryhigh. To correctly control the deflection, a mark position on a stagethat is provided with a laser interferometer is determined under acertain deflection condition, and then the deflection condition isdetermined by moving the mark. A corresponding relationship between thedeflection condition and the actual mark position is determined byrepeating this operation, to thereby adjust a deflection system so thatthe deflection position is located at a prescribed position.

A mark may be produced by forming a very small hole in a heavy metalthin film. The signal polarity is inverted at the mark. Further, aninflow current may be measured by using a minute Faraday cup structureas a mark. FIG. 12a shows another exemplary beam measurement using aconventional mark. FIGS. 12b-12 c are graphs showing the signalintensity of reflected electron signals. A position is determined basedon a signal as shown in FIG. 12b that is obtained by scanning a singlemark 122 with a beam 121 as shown in FIG. 12a. The middle of two peakpositions may be obtained, for example, by differentiating a mark signalas shown in FIG. 12c.

A signal obtained by scanning a mark with a beam typically includesconsiderable noise. To eliminate such noise, mark signals are obtainedby scanning the mark with a beam many times and superimposing thosesignals one on another. In this case, it takes a long time to obtainsufficient accuracy. Further, applying a beam to the same location manytimes causes the mark and its vicinity to be heated locally. Theresulting thermal expansion of the mark and the mark substrate may lowerthe accuracy.

As described above, the conventional method of adjusting the opticalaxis, the deflection position, the rotation, or the like of an energybeam by using a single mark has various problems, such as failure toobtain sufficiently high adjustment accuracy and the long time requiredto make adjustments.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesin the art, and an object of the invention is therefore to provide anoptical system adjusting method in an energy beam apparatus which canperform, correctly and in a short time, an optical system adjustment foroptimizing the optical axis, the deflection position, or the rotation ofan energy beam.

The present invention provides a method for adjusting an optical systemof an energy beam apparatus, comprising preparing a mark having aone-dimensional or two-dimensional periodic structure; detecting a marksignal by scanning the mark with an energy beam one-dimensionally ortwo-dimensionally; and determining a variation in a positionalrelationship between the mark and a beam scanning region based on aphase variation of the mark signal.

In one aspect, a first mark signal is detected by scanning, with anenergy beam, the mark that is set on the optical axis of the opticalsystem. A second mark signal is detected by scanning, with an energybeam, the mark that is located at a position that is deviated from theoptical axis of the optical system. A deviation of a deflection positionis determined based on a phase difference between the first and secondmark signals.

In another aspect, a first mark signal is detected by scanning, with anenergy beam, a mark that is set on the optical axis of the opticalsystem. A second mark signal is detected by scanning, with an energybeam, the mark in a state in which a driving condition of a lens that isbeing axially aligned is changed. A deviation between the energy beamoptical axis and the axis of the lens is determined based on a phasedifference between the first and second mark signals.

In another aspect, small fields that are smaller than energy beamdeflection-test regions are set so that boundaries of adjacent ones ofthe small fields are in contact with each other. For adjacent smallfields, mark signals are detected in an overlap region ofdeflection-test regions by using marks having the same periodicstructure. The optical system is adjusted so that the two mark signalsfor the adjacent small fields coincide with each other.

In another aspect, a phase deviation of the mark signal is detectedbased on a phase deviation of a moiré signal that is obtained bycalculating the product of the mark signal and a reference signal havinga different frequency than the mark signal.

In another aspect, an offset-removed component of the mark signal isbinarized. A phase deviation of the mark signal is detected based on aphase difference signal that is obtained by calculating the product ofthe binarized mark signal and a binarized reference signal having thesame frequency as the mark signal and averaging a resulting productsignal.

In another aspect, the mark has a two-dimensional periodic structure. Adeviation in the rotational direction of a beam deflection region isdetected based on a two-dimensional distribution that is obtained basedon phase variations of periodic components of a mark signal distributionthat correspond to the period(s) of the mark.

In another aspect, the mark has a two-dimensional periodic structure. Asecond or higher order deviation of a beam deflection region from adesigned deflection region is detected based on a two-dimensionaldistribution that is obtained based on phase variations of periodiccomponents of a mark signal distribution that correspond to the periodsof the mark.

In another aspect, a phase deviation of the mark signal based on a phasedifference between moiré signals that are obtained for two referencesignals that are higher and lower, respectively, in frequency than themark signal.

In another aspect, a phase deviation of the mark signal is detectedbased on a phase difference signal that is obtained by calculating theproduct of the mark signal and a reference signal having the samefrequency as the mark signal and averaging a resulting product signal.

In another aspect, the product of the mark signal and the referencesignal is obtained by modulating the energy beam intensity at thefrequency of the reference signal.

The energy beam may be an electron beam, an ion beam, a neutral particlebeam, or a photon beam.

The present invention provides adjustment of, for example, the beamposition on a sample correctly in a short time by determining avariation in the positional relationship between a mark and a beamscanning region based on a phase variation of a mark signal, therebycontributing to, for example, an increase of the rate of operation of anenergy beam apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1 e show mark patterns that are used in a first embodiment ofthe present invention;

FIGS. 2a and 2 b are graphs showing an example of a periodic mark signaland its fundamental-wave component, respectively;

FIGS. 3a and 3 b are graphs showing the fundamental-wave component of amark signal and that of a phase-deviated signal, respectively;

FIG. 4 is a graph showing phase difference dependence of the product ofa rectangular-wave mark signal and a reference signal;

FIG. 5 is a graph showing phase difference dependence of a phasedifference signal that is obtained from the product of thefundamental-wave component of a mark signal and a reference signal;

FIG. 6a is a graph showing the intensity of a signal obtained from theproduct of the fundamental-wave component of a mark signal and areference signal;

FIG. 6b is a graph showing the intensity of the fundamental-wavecomponents of mark signals obtained at two different points and acorresponding moiré signal;

FIG. 7 is a graph showing moiré signals obtained by using referencesignals that are higher and lower in frequency than the fundamental-wavecomponent of a mark signal;

FIG. 8 shows how a two-dimensional moiré signal varies as mark scanningis rotated;

FIG. 9 is a schematic view showing an adjusting method for beamconnection in an overlap region of deflection-possible regions foradjacent small regions;

FIG. 10 is a schematic view showing a tracking adjustment for a stagethat is moved continuously;

FIG. 11 shows an exemplary beam measurement using a conventional mark;

FIG. 12a—shows another exemplary beam measurement using a conventionalmark; and

FIGS. 12b-12 c are graphs showing the signal intensity of reflectedelectron signals using a conventional mark.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is hereinafter described in detail by usingillustrated embodiments.

Embodiment 1

FIGS. 1a-1 e show mark patterns according to a first embodiment of thepresent invention. In the example of FIG. 1a, a sample having a mark maybe a chromium mask in which a conductive film is formed on a chromiumlight shield film as an undercoat that is formed on a glass substrate.The mark may be produced by etching a chromium light shield film in acheckered pattern having a constant period S. Mark patterns shown inFIGS. 1b-1 e can also be used.

Determining a beam position by using the mark shown in FIG. 1a is nowdescribed. Although in this example an electron beam is assumed as anenergy beam, the energy beam is not limited to an electron beam and maybe, for example, light, an ion bean, or a neutral particle beam. A stagethat is mounted with a sample is moved so that a beam strikes the centeror its vicinity of the mark when the beam is located at an origin (0, 0)of the deflection position. In this state, a reflected electron signalis captured that is obtained when a deflector scans the mark with a beamin the vertical and horizontal directions with a deflector. Theresulting signal is periodic in both vertical and horizontal directions,as shown in FIG. 2a. The fundamental component of sinusoidal componentsof the signal thus obtained is shown in FIG. 2b.

Then, the mark position is moved to a position (x1, y1) by moving thestage. A mark movement distance is measured accurately by a laserinterferometer that is provided on the stage. A beam is deflected to theabove position, and scanning is performed with a beam in the verticaland horizontal directions with the same widths (the above position iscentered) as in the above-case where the mark was located at the origin(0, 0). Referring to FIG. 3a, there is shown a graph of thefundamental-wave component of a mark signal. A sinusoidal component of asignal that is obtained in this state is equal in phase to the signalthat was obtained at the origin (0, 0). Referring to FIG. 3b, there isshown a fundamental-wave component of a phase-deviated signal. However,if the deflection position deviates from the desired position even by asmall value, a phase deviation occurs between the signals as shown inFIG. 3b. Therefore, a deviation of the deflection position can bemeasured based on a phase deviation between a first mark signal 31 thatis obtained at the origin (0, 0) and a second mark signal 32 that isobtained at the position (x1, y1).

Methods (1-a) to (1-d) described below can be used as a phase deviationdetecting method. Since in many cases a mark signal includes an offsetvalue, a signal obtained by subtracting an offset value that isdetermined in advance from a mark signal is used as a new mark signal.Another desirable measure is to remove a temporally invariable componentof a mark signal by causing the mark signal to pass through a capacitor,for example.

Phase Deviation Detecting Method (1-a):

A signal obtained is binarized, that is, converted into a signal havingvalues 0 and 1, to generate a rectangular wave. The product of a binarydistribution obtained from a signal at the origin (0, 0) and a binarydistribution obtained from a signal at (x1, y1) is calculated and theaverage value of a resulting distribution is calculated.

FIG. 4 is a graph showing the phase difference dependence of the productof a rectangular-wave signal and a reference signal. If the-phases areexactly equal to each other, the average value is 0.5 as shown in FIG.4. If the phases are different from each other by 180°, the averagevalue is 0. If the phase difference is between 0° and 180°, the averagevalue is a value between 0 and 0.5. Binarizing a signal increases thephase detection sensitivity. Alternatively, signal values themselves maybe used. However, in this case, although the product varies with thephase variation, the average value varies with the offset value and theamplitude.

Phase Deviation Detecting Method (1-b):

A phase component of a signal obtained is detected by subjecting thesignal to a Fourier transform in a limited interval, and a variation inthe detected phase component is determined. The fundamental component ofa signal is now represented by I sin(kx+α). If it is multiplied by areference signal sin(kx) and then averaged over n periods (n: naturalnumber), all of an offset component and harmonic components of thesignal become 0, and finally a phase difference signal 0.5 nI cos α isobtained.

FIG. 5 is a graph showing the variation of the phase difference signalwith α. A desired beam deflection position is obtained when the phasedifference signal is maximized by moving the beam deflection position. Aphase difference signal may be directly obtained by modulating theintensity of an energy beam itself and integrating a resulting signalinstead of multiplying a mark signal by a reference signal.

Phase Deviation Detecting Method (1-c):

FIG. 6a is a graph showing the intensity of a signal obtained from theproduct of the fundamental-wave component of a mark signal and areference signal. FIG. 6b is a graph showing the intensity of thefundamental-wave components of mark signals obtained at two differentpoints and a corresponding moiré signal. The fundamental component of asignal obtained is now represented by I sin(kx+α). As shown in FIG. 6a,if the fundamental component is multiplied by a reference signalsin(k′x) that is slightly deviated in frequency, a resulting signal isgiven by

0.5 I cos {(k−k′)x+α}−0.5 I cos {(k+k′)x+α}.

As for the first term, values of x that give the same phase are deviatedfrom each other by −Δα/(k−k′) for a variation Δα of the phase differenceα. Now assume that the first term is a new signal (moiré signal). Then,as shown in FIG. 6B, its phase deviation is k/(k−k′) times larger thanthe phase deviation of the original signal. Although the sign ofk/(k−k′) varies with the magnitude relationship between k and k′, in thefollowing description the magnification factor is assumed to be anabsolute value unless otherwise specified. A desired beam deflectionposition is obtained by adjusting the beam deflection position so thatthe phase variation between moiré signals at the origin (0, 0) and theposition (x1, y1) is minimized.

Next, the second term is considered. For a subject value of x, averagingis performed over a range of x−L/2 to x+/2 where L satisfies(k−k′)L=(2n−1)π(n: integer).

With exception of the common coefficient 0.5 nI, $\begin{matrix}{\begin{matrix}\left( {{average}\quad {value}} \right. \\\left. {{of}\quad {first}\quad {term}} \right)\end{matrix} = {\left( {1/L} \right)\quad {\int{\cos \quad \left\{ {{\left( {k - k^{\prime}} \right)x} + \alpha} \right\} {x}}}}} \\{\quad {= {\left\{ {1/{L\left( {k - k^{\prime}} \right)}} \right\}\left\lbrack {{\sin \left\{ {{\left( {k - k^{\prime}} \right){L/2}} + {\left( {k - k^{\prime}} \right)x} + \alpha} \right\}} -} \right.}}} \\\left. \quad {\sin \left\{ {{{- \left( {k - k^{\prime}} \right)}{L/2}} + {\left( {k - k^{\prime}} \right)x} + \alpha} \right\}} \right\rbrack \\{\quad {= {\left\{ {1/{L\left( {k - k^{\prime}} \right)}} \right\}\left\lbrack {{\cos \left\{ {{\left( {k - k^{\prime}} \right)x} + \alpha} \right\}} +} \right.}}} \\\left. \quad {\cos \left\{ {{\left( {k - k^{\prime}} \right)x} + \alpha} \right\}} \right\rbrack \\{\quad {= {\left( {2/\pi} \right)\cos {\left\{ {{\left( {k - k^{\prime}} \right)x} + \alpha} \right\}.}}}} \\{\begin{matrix}\left( {{Average}\quad {value}} \right. \\\left. {{of}\quad {second}\quad {term}} \right)\end{matrix} = {\left( {1/L} \right){\int{\cos \left\{ {{\left( {k + k^{\prime}} \right)x} + \alpha} \right\} {x}}}}} \\{\quad {= {\left\{ {1/{L\left( {k + k^{\prime}} \right)}} \right\}\left\lbrack {{\sin \left\{ {{\left( {k + k^{\prime}} \right){L/2}} + {\left( {k + k^{\prime}} \right)x} + \alpha} \right\}} -} \right.}}} \\\left. \quad {\sin \left\{ {{{- \left( {k + k^{\prime}} \right)}{L/2}} + {\left( {k + k^{\prime}} \right)x} + \alpha} \right\}} \right\rbrack \\{\quad {= {\left\{ {1/{L\left( {k + k^{\prime}} \right)}} \right\}\left\lbrack {\sin \left\{ {{kL} + {\left( {{- k} + k^{\prime}} \right){L/2}} +} \right.} \right.}}} \\{\left. \quad {{\left( {k + k^{\prime}} \right)x} + \alpha} \right\} - {\sin \left\{ {{- {kL}} - {\left( {{- k} + k^{\prime}} \right){L/2}} +} \right.}} \\\left. \left. \quad {{\left( {k + k^{\prime}} \right)x} + \alpha} \right\} \right\rbrack \\{\quad {= {\left\{ {1/{L\left( {k + k^{\prime}} \right)}} \right\}\left\lbrack {{{- \cos}\left\{ {{kL} + {\left( {k + k^{\prime}} \right)x} + \alpha} \right\}} +} \right.}}} \\\left. \quad {\cos \left\{ {{- {kL}} + {\left( {k + k^{\prime}} \right)x} + \alpha} \right\}} \right\rbrack \\{\quad {= {\left\{ {2/{L\left( {k + k^{\prime}} \right)}} \right\} \sin \left\{ {{\left( {k + k^{\prime}} \right)x} + \alpha} \right\} {{\sin ({kL})}.}}}}\end{matrix}$

In the above equations, each integral is calculated from a lower limitx−L/2 to an upper limit x+L/2.

Therefore, the average value of the second term becomes 0 if kL=2 mπ (m:natural number). As is apparent from the two conditions (k−k′)L=(2n−1)π,and kL=2 mπ, it is desirable that k′ and L be determined so as tosatisfy

kL=2mπ, (k−k′)L=±π.

For example, if m=5 and k−k′=π/L,

k/(k−k′)=10

is obtained.

Since the average value of the second term decreases approximately ininverse proportion to kL, it is desirable that m be a large value.Although an offset value may be removed in advance from a mark signal,it is removed in the above process of obtaining a moiré signal and thedesirable condition in the above averaging process. Further,high-frequency noise components are removed by the above averagingprocess.

A signal

0.5 I[ cos {(k−k′)x+α}−cos {(k+k′)x+α}]

may be obtained by modulating the intensity of an energy beam itself sothat the variation component of a mark signal that is obtained when amark having uniform reflectance is scanned with a beam becomes Isin(k′x). This process may be used instead of calculating the product ofa mark signal and a reference signal that is incorporated in theapparatus. In this case, it may be desirable to remove a temporallyinvariable constant at the time of obtaining a signal because an offsetcomponent remains even after the averaging process.

Phase Deviation Detecting Method (1-d):

FIG. 7 is a graph showing the moiré signals obtained by using referencesignals that are higher and lower in frequency than the fundamental-wavecomponent of a mark signal. The fundamental component of a signalobtained is now represented by I sin(kx+α). It is multiplied byreference signals sin(k′x) and sin(k″x) that are slightly higher andlower, respectively, in frequency than the fundamental component,whereby moiré signals are obtained for the respective reference signals.Moiré signals are extracted in the same manner as in the method (1-c).If a variation between a phase difference between the two moiré signalsat point A and that at point B is determined as shown in FIG. 7, thisvariation is larger than a phase variation obtained by the method (1-c).

If the absolute values of the two phase differences obtained in theabove manner are made equal to each other, then k can be determined withhigh accuracy because k′ and k″ can be determined with high accuracy. Adesired beam deflection position is obtained by adjusting the beamdeflection position so that the phase differences of moiré signals atthe origin (0, 0) and the position (x1, y1) are made equal to eachother.

Beam deflection positions are examined at different mark positions byrepeating one or more of the above-described methods, and adjustmentsare so made that the beam deflection positions fall within an allowablerange for a desirable value. This enables highly accurate control of thebeam deflection position.

Embodiment 2

This embodiment relates to alignment of the beam optical axis and thelens axis. First, the mark that has been described in the firstembodiment is moved to the origin (0, 0) of the deflection position. Atthis position, a signal is obtained by scanning a beam in both verticaland horizontal directions. Then, another signal is obtained in a similarmanner after changing the focal length of a lens that is to be axiallyaligned by changing an excitation magnetic or electric field for thelens by a very small amount.

Then, a change of the beam position on the stage position is detectedbased on the thus-obtained two signals according to any of the detectionmethods described in the first embodiment. The axes of the lens and abeam are aligned with each other by adjusting an axial alignment coil orelectrode so that the change of the beam position is minimized when thelens focal length is varied around a set value.

If a fluctuation of the beam position has been measured by anothertechnique based on a moiré signal that was obtained with a constant lensfocal length, a fluctuation of the stage position may also bedetermined.

Embodiment 3

This embodiment relates to alignment of the coordinate axes of beamdeflection and those of a mark. First, a two-dimensional image of acheckered mark having approximately the same area as a beam deflectionregion is obtained by deflecting a beam with the center of the mark usedas the origin. The angular spatial frequency is represented by the term“k.”

FIG. 8 shows the variation of a two-dimensional moiré signal as the markscanning is rotated. Now assume that the coordinate axes of the beamdeflection is rotated by an angle θ from those of the mark. If a moirésignal is displayed two-dimensionally with an assumption that theangular spatial frequency of a reference signal is k′ in both axes, themoiré signal rotates by k/(k−k′)θ when θ is small. Therefore, a rotationof the axes can be detected easily.

If two moiré signals are determined by using two reference signals inwhich k′<k and k″>k, an angular deviation between the two moiré signalsis approximately given by [(k′−k″)/{(k−k′)(k−k″)}]θ. If k and k′ are sodetermined that k/(k−k′)θ becomes equal to k/(k″−k)θ, the angulardeviation is given by {(k′+k″)/Δk}θ where Δk=k−k′=k″−k and can bedetermined with high accuracy. As θ increases, the frequency of a marksignal increases, and hence the period of the moiré signals becomesshorter. The period of the moiré signals is longest when θ=0.

As another embodiment, the period of a moiré signal may be measured, andadjustments made so that the period of the moiré signal becomes longest.The pitch of two-dimensional scanning with a beam may be set toapproximately an integral multiple of the period of a periodic mark, anda positional deviation may be detected along each scanning line.

Embodiment 4

A two-dimensional image of a checkered mark having approximately thesame area as a beam deflection region is obtained by deflecting a beamwith the center of the mark used as the origin. The angular spatialfrequency is represented by the term “k.” Now assume that an actual beamdeflection position (X, Y) is deviated from a desired position (x, y) by(ΔX, ΔY), that is, X=x+ΔX and Y=y+ΔY. Consideration is made of a casewhere characteristic lengths of distributions of ΔX and ΔY aresufficiently longer than the wavelength of a moiré signal.

Intersections of lines where a two-dimensional moiré signal is maximumare now called moiré signal lattice points. Alternatively, moiré signallattice points may be defined as intersections of lines where atwo-dimensional moiré signal is minimum or points where the signal is 0.Consideration is now given to a distribution of lattice point positionsin a two-dimensional moiré signal. The angular spatial frequency of anideal moiré signal is represented by Δk and the angular spatialfrequency of a reference signal is represented by k. It is assumed thata lattice point corresponding to one two-dimensional moiré signallattice point (x1, y1) in a case where ΔX=0 and ΔY=0 are satisfied atevery point is moved to (x1+dX1, y1+dY1) on the two-dimensional moirésignal.

Let k_(x) and k_(y) represent angular spatial frequencies of a marksignal in the x-direction and the y-direction in the vicinity of ameasurement point and k′ represent an angular spatial frequency of thereference signal in each of the x-direction and the y-direction. Then,ΔX and ΔY are given as follows:

ΔX=−dX1(k _(x) −k′)/k _(x)

ΔY=−dY1(k _(y) −k′)/k _(y)

Since lattice point positions can be changed by changing the phase ofthe reference signal, (ΔX, ΔY) distributions can be obtained easily.

Deflection parameters are adjusted based on the thus-obtained (ΔX, ΔY)distributions so that the deviation between the actual deflectionposition (X, Y) and the desired position (x, y) is within an allowablerange in the entire deflection region. Specifically, a correction of(−ΔX, −ΔY) is made for the desired deflection position (x, y) with anassumption that, for example, ΔX and ΔY are given as follows:

ΔX=a 1·x+b 1·y+c 1·x·x+d 1·x·y+e 1·y·y

ΔY=a 2·x+b 2·y+c 2·x·x+d 2·x·y+e 2·y·y

Accordingly, the beam deflection position may be controlled with highaccuracy.

Embodiment 5

This embodiment relates to a method for adjusting the deflectionposition in each field to connect adjacent fields.

FIG. 9 is a schematic view showing an overlap region ofdeflection-possible regions for adjacent small regions. Adjacent smallfields on a sample are denoted by Aw and Bw, and electron beamdeflection regions corresponding to the small fields Aw and Bw aredenoted by Ad and Bd, respectively. The deflection regions Ad and Bdhave an overlap region AB. A two-dimensional mark is disposed in theoverlap region AB as shown in FIG. 9. While electron beam deflection isperformed in the region Ad, the region AB is scanned with the beam inthe x-direction and the y-direction, and moiré signals M1x and M1y areobtained based on a resulting mark signal.

On the other hand, while electron beam deflection is performed in theregion Bd, the region AB is scanned with the beam in the x-direction andthe y-direction and moiré signals M2x and M2y are obtained based on aresulting mark signal. If the beam deflection is so adjusted that themoiré signals M1x and M2x are equalized in phase and the moiré signalsM1y and M2y are equalized in phase, the beam deflection positionscoincide with each other at the boundary between the writing fields Awand Bw. In this manner, the writing fields Aw and Bw can be connected toeach other smoothly.

Of course, adjustments may be made so that two-dimensional moiré signalsthat are obtained by two-dimensionally scanning a mark coincide witheach other, instead of scanning a mark in two directions.

Embodiment 6

This embodiment relates to a method for adjusting the beam deflectionwidth accurately. Consideration is given to a variable shaping beam or acharacter beam. In a state in which a small mark is placed on a sample,a beam shape is measured first. Then, a one-dimensional ortwo-dimensional mark that has been formed accurately in advance isscanned with a beam.

It is assumed that the period of the mark is determined correctly. Forexample, if the pitch of the mark is 1 μm and the beam deflection widthis 10 μm, nine pulses are obtained by one beam scan. The number ofpulses varies with the beam deflection width. That is, the signal periodvaries with the beam deflection width. By utilizing this fact, the beamdeflection width is adjusted and the beam application positions aredetermined accurately.

Specifically, the signal period is determined correctly according to,for example, the method (1-d) that was described in the firstembodiment. The absolute value of the beam deflection distance isdetermined by comparing the thus-determined signal period with a markperiod that has been measured in advance. Positions between consecutiveshots are determined based on this deflection distance and a measuredbeam shape. Accordingly, consecutive beam application positions may bedetermined correctly.

Embodiment 7

In writing apparatuses, to increase the writing speed, it is desirablethat writing be performed while a stage that is mounted with a sample ismoved continuously. For this purpose, a beam is moved so that it remainsapplied to the same positions on a sample by correctly measuringpositions on a moving sample stage with a laser interferometer, forexample. This is called tracking. The method of the present inventionalso makes it possible to perform a tracking adjustment with highaccuracy.

FIG. 10 is a schematic view illustrating a tracking adjustment for astage that is moved continuously. A lattice-shaped mark 101 is providedon a stage and is two-dimensionally scanned with a beam 102, in acruciform-like manner, or one-directionally along a movement direction.Reflected electrons 103 coming from the mark 101 are detected by anelectron detector 104. At this time, if the beam scanning region and themark are relatively deviated from each other, a deviation is detected inthe phase of a moiré signal. Therefore, a beam deflection adjustment isperformed so that a phase shift of the moiré signal is in a small,allowable range.

Conversely, it is possible to detect a fluctuation of the stagemeasurement accuracy and a fluctuation of the deflection distance, basedon the relationship between a deflection control signal and the stageposition that is measured by the laser interferometer 105 and a phasevariation of a moiré signal.

The present invention is not limited to the above-described embodiments.The above embodiments are mainly directed to the methods for measuring adeviation in the positional relationship between a beam deflectionregion and a mark. However, in the case of the method (1-b) of the firstembodiment, if the size of a beam deflection region on a mark isdeviated from a prescribed value, the frequency of a measured marksignal deviates from a prescribed value k. Therefore, when the mark ismanufactured with a necessary accuracy, it is desirable that the size ofthe deflection region be so set that the angular spatial frequency ofthe mark signal becomes the prescribed value k.

Also in the case of the method (1-c) of the first embodiment, thefrequency of a moiré signal similarly deviates from a prescribed value.Therefore, the size of a deflection region of a beam for scanning of amark can be adjusted by determining the size of the deflection region sothat the frequency of a moiré signal becomes a prescribed value.

Although the above embodiments are directed to the case of using acheckered mark, the present invention is not limited to such a case. Forexample, as shown in FIGS. 1b and 1 c, a one-dimensional line-and-spacemark can be used for one-dimensional positioning. Instead of using acheckered mark, line-and-space marks in the x-direction and they-direction may be provided perpendicularly to each other as shown inFIGS. 1d and 1 e. A beam position may be measured by providingline-and-space marks in the x-direction and the y-direction. A mark mayeven be formed by arranging triangular or hexagonal units, for example.A mark preferably has a periodic structure in a measurement direction.

The present invention is not limited to the electron beam lithographyapparatus, and can be applied to adjustment of optical systems ofvarious kinds of energy beam apparatuses. That is, the energy beam isnot limited to an electron beam, and may be an ion beam, a neutralparticle beam, or a photon beam. The present invention can be modifiedin other various ways without departing from the sprit and scope of theinvention.

As described above, the present invention allows an optical system to beadjusted, correctly and in a short time, for optimizing the opticalaxis, the deflection position, the rotation, or the like of an energybeam by determining a variation in the positional relationship between amark and a beam scanning region based on a phase variation of a marksignal, thereby contributing to, for example, an increase of the rate ofoperation of various kinds of energy beam apparatuses.

What is claimed is:
 1. A method for adjusting an optical system of anenergy beam apparatus, comprising: preparing a mark having aone-dimensional or two-dimensional periodic structure; detecting a firstmark signal by scanning said mark with an energy beam, said mark beingset on an optical axis of said optical system; detecting a second marksignal by scanning said mark with an energy beam, said mark being in astate for changing a driving condition of a lens to be axially aligned;and determining a deviation between an energy beam optical axis and anaxis of said lens based on a phase deviation between said first andsecond mark signals.
 2. A method for adjusting an optical system of anenergy beam apparatus according to claim 1, further comprising detectingsaid phase deviation of said first and second mark signals based on aphase deviation of moiré signals of said first and second mark signalthat are obtained by calculating said first and second mark signals anda reference signal having a different frequency than said first andsecond mark signals.
 3. A method for adjusting an optical system of anenergy beam apparatus according to claim 2, in which said moiré signalsare obtained for two reference signals that are higher and lower,respectively, in frequency than said first and second mark signals.
 4. Amethod for adjusting an optical system of an energy beam apparatusaccording to claim 1, further comprising: binarizing an offset-removedcomponent of said first and second mark signals; and detecting a phasedeviation of said first and second mark signals based on a phasedeviation signal that is obtained by calculating a product of said firstand second binarized mark signals and averaging a resulting productsignal.
 5. A method for adjusting an optical system of an energy beamapparatus according to claim 1, further comprising: detecting a phasedeviation of said first and second mark signals based on a phasedeviation signal that is obtained by calculating a product of said firstand second mark signals and averaging a resulting product signal.
 6. Acomputer useable medium for causing an optical system to execute themethod of claim 1.